Infrared remote control transmitter

Hi,
I'm quite new to electronics, but I have to make a presentation about infrared remote control for my (simple) electronics course at college.
I found a few circuits already, but I don't really understand how exactly a signal is generated using an encoder/decoder IC.
Could anyone explain/clarify?
Thank you

The signal is a series of pulses coded for each command. Here is an explanation of one type of protocol.

The code is likely generated by having the code stored in permanent memory in the transmitter microprocessor. The button you press determines which code in memory is accessed and sent out from the transmitter. The receiver has a similar memory and it matches the incoming code with the identical one in its memory to determine which function to activate.